我正尝试编写一个用于让Beaglebone上的LED闪烁的C程序。我知道我可以使用sysfs方法...但我想看看是否可以通过映射/dev/mem的物理地址空间来获得相同的结果。
我有一个名为beaglebone_gpio.h的头文件,其中包含以下内容:
#ifndef _BEAGLEBONE_GPIO_H_
#define _BEAGLEBONE_GPIO_H_
#define GPIO1_START_ADDR 0x4804C000
#define GPIO1_END_ADDR 0x4804DFFF
#define GPIO1_SIZE (GPIO1_END_ADDR - GPIO1_START_ADDR)
#define GPIO_OE 0x134
#define GPIO_SETDATAOUT 0x194
#define GPIO_CLEARDATAOUT 0x190
#define USR0_LED (1<<21)
#define USR1_LED (1<<22)
#define USR2_LED (1<<23)
#define USR3_LED (1<<24)
#endif
接下来我有我的C程序,gpiotest.c
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "beaglebone_gpio.h"
int main(int argc, char *argv[]) {
volatile void *gpio_addr = NULL;
volatile unsigned int *gpio_oe_addr = NULL;
volatile unsigned int *gpio_setdataout_addr = NULL;
volatile unsigned int *gpio_cleardataout_addr = NULL;
unsigned int reg;
int fd = open("/dev/mem", O_RDWR);
printf("Mapping %X - %X (size: %X)\n", GPIO1_START_ADDR, GPIO1_END_ADDR, GPIO1_SIZE);
gpio_addr = mmap(0, GPIO1_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, GPIO1_START_ADDR);
gpio_oe_addr = gpio_addr + GPIO_OE;
gpio_setdataout_addr = gpio_addr + GPIO_SETDATAOUT;
gpio_cleardataout_addr = gpio_addr + GPIO_CLEARDATAOUT;
if(gpio_addr == MAP_FAILED) {
printf("Unable to map GPIO\n");
exit(1);
}
printf("GPIO mapped to %p\n", gpio_addr);
printf("GPIO OE mapped to %p\n", gpio_oe_addr);
printf("GPIO SETDATAOUTADDR mapped to %p\n", gpio_setdataout_addr);
printf("GPIO CLEARDATAOUT mapped to %p\n", gpio_cleardataout_addr);
reg = *gpio_oe_addr;
printf("GPIO1 configuration: %X\n", reg);
reg = reg & (0xFFFFFFFF - USR1_LED);
*gpio_oe_addr = reg;
printf("GPIO1 configuration: %X\n", reg);
printf("Start blinking LED USR1\n");
while(1) {
printf("ON\n");
*gpio_setdataout_addr= USR1_LED;
sleep(1);
printf("OFF\n");
*gpio_cleardataout_addr = USR1_LED;
sleep(1);
}
close(fd);
return 0;
}
输出结果为:
Mapping 4804C000 - 4804DFFF (size: 1FFF)
GPIO mapped to 0x40225000
GPIO OE mapped to 40225134
GPIO SEDATAOUTADDR mapped to 0x40225194
GPIO CLEARDATAOUTADDR mapped to 0x40225190
GPIO1 configuration: FE1FFFFF
GPIO1 configuratino: FE1FFFFF
Start blinking LED USR1
ON
OFF
ON
OFF
...
但我看不到LED闪烁。
从程序的输出可以看出,配置是正确的,FE1FFFFF 是一致的,因为 GPIO1_21、GPIO1_22、GPIO1_23 和 GPIO1_24 都被配置为输出,每一个都驱动着一个 LED。
对于原因有什么想法吗?